Thats a question that can have many different answers. Some say litely coat the internals before assembly, some say dump a pile oil in there before assembly. I find the latter to be a pain and not needed unless you want to smoke up the place and crank your hiny off till she finally starts. A lite coat of 2 cycle oil is all I use in the shop on customer rebuilds, I mean very lite. Too date I've had no engine failures come back.
Even so I've been doing alittle experiment on a few of my own saws. I've rebuilt several saws the past year or so I got for free, around 10 or so. I assembled them with no type of engine oil but instead merely used just a little bit Stihl penetrating oil out of a spray can. I litely sprayed all the bearings, gave the cylinder a good spray and wipe the excess out. I sprayed the rings and skirts fairly wet and wipe off the excess threw them babies together. The result, I can't see any differance than the customer saws I use engine oil on the internals before assembly other than a helluva lot less smoke and easier starting on the first start up after rebuild. Will they last, they seem to far as I can tell. I've sold a few of these freebies rebuilt using only penetrating oil cheap, price of the parts, to a good buddy of mine and he runs the living hell out of them. Too date no engine failures. So who knows.
Thats not saying don't use oil on your rebuild, its saying oiling the internals by dumping oil all over is not needed. A lite coat is all thats needed. I suspect less is alot better than alot. I wonder if oiling the internals is needed at all on assembly other than making the piston slip in the cylinder easier but thats me, not the majority on the subject. Oiling seems to be the norm and I'm sure it doesn't hurt anything if used moderately. Too much is a mess, a hard start up and a smoke stack when it does start..